1. Field of the Invention
This invention relates to a catalytic method for the preparation of N,N'-dimethyl piperazine. More particularly, this invention relates to a catalytic method for the substantially selective manufacture of N,N'-dimethyl piperazine from piperazine and methanol. Still more particularly, this invention is directed to the use of a titania catalyst to which a minor amount of phosphorus has been thermally chemically bonded at the surface thereof in the form of phosphate phosphate linkages to substantially selectively catalyze the conversion of methanol and piperazine to N,N'-dimethyl piperazine.
2. Prior Art
The catalysts used in the practice of the process of the present invention are disclosed in Vanderpool European patent application Ser. No. 83,307,520.3 published Aug. 28, 1984, wherein they are disclosed as useful in promoting the reaction of ethylenediamine with ethanolamine to provide essentially linear polyethylenepolyamine reaction products. Minor quantities of cyclic products are also formed.
It has heretofore been proposed to prepare N,N'-dimethylpiperazine by a variety of techniques. For example, Steele U.S. Pat. No. 2,868,791 discloses a process for the preparation of N,N'-dimethylpiperazine by the pressured reaction of N-methylethanolamine with carbon dioxide. In the example, an aqueous solution of N-methylethanolamine was saturated with carbon dioxide and heated at 160.degree.-170.degree. C. for 20 hours at a pressure of 500-580 psia to provide a crude reaction mixture containing N,N'-dimethylpiperazine.
Godfrey U.S. Pat. No. 3,037,025 discloses a process for the preparation of N-alkyl substituted piperazines such as N,N'-dimethylpiperazine by reacting monoethanolamine with methylamine at an elevated temperature and pressure in the presence of a nickel, copper, chromia hydrogenation catalyst in the presence of hydrogen. There is a similar disclosure in Godfrey U.S. Pat. No. 3,037,025.
Schulze U.S. Pat. No. 4,066,649 discloses a process for the catalytic production of N,N'-(dimethyl) piperazines by reacting a primary 1-amino-2-alkanol such as monoethanolamine with methyl alcohol. The catalyst that is used is a phosphorus containing substance such as acidic metal phosphate, a compound of phosphorus or phosphoric acid, alkyl or aryl phosphate or phosphite esters.
A process for the production of N-alkylated cyclic alkyleneimines such as N-methyl piperazine from an alcohol such as methanol and a cyclic amine such as piperazine is disclosed in Dockner et al. U.S. Pat. No. 4,105,657. The catalyst is a high surface area SiO.sub.2 /P.sub.2 O.sub.5 catalyst prepared, for example, by reacting 0.1 to 20% of phosphoric acid with a silic acid hydrogel.